GeologyRocks

I just wanted to tack on an amendment.

I've remembered that there are huge frozen methane 'deposits' in the frozen tundra of Siberia which are projected to melt and deliver vast quantities of methane into the atmosphere if the global temperature rises by X^oC. This would obviously lead to a positive feedback loop.

For the purposes of the question it would be good to know if the estimated temperature rise is likely to occur if all the oil and gas was to be used (my limited understanding is that it is), if so at what point, and if so what the effect of all this methane would be.

By the way, I am just looking at a discussion point here rather than fully quantified answers (although they're great too if you've got them). It's been a bit quiet on here of late and I thought this might get the ball rolling again.

An interesting question. I think the main point to bear in mind is that although CO2 levels will theoretically peak, and temperatures reach a predictable maxima, it is the subsequent effects of this rise that will cause further probems, a point you refer to in mentioning methane Tundra deposits.

In essence, it is the interelatedness of the system that is the problem, for instance, Professor Tony Hallam of the University of Birmingham suggests that vast quantities of methane hydrates buried beneath the ocean floors could be released by a relatively modest increase in temperature.

Furthermore, the increase in desertification as the result of increased temperatures reduces primary production so carbon is not removed from the atmosphere.

Just to add a little spice to the discussion, some conspiracy theorists advocate that large oil companies far from developing alternative fuels etc, have historically supressed such innovation to maintain their monopoly and dependency on oil/gas and charge ever increasing amounts. Ask yourself, does the relatively recent increase in global oil prices really reflect increased production costs, or any factor other than decreasing product supply? Although the figures derived fom the website below seem to suggest otherwise...

 http://www.eia.doe.gov/aer/txt/ptb1105.html

 Oh, and your question about the effect of methane is quite straightforward:

"Methane is over 20 times more effective in trapping heat in the atmosphere than carbon dioxide (CO₂) over a 100-year period..." [http://www.epa.gov/methane/]

However, methane has a relatively short half-life approx 14ish yrs, decaying into, you've guessed it, CO2 and water (which is also integral to the greenhouse effect, natural or anthropogenic!)

I think that while it seems easy to view this increase in CO2 as a train headed in the same direction for eternity, but, just like economic depressions, things eventually go the other way.  The earth has been through these cycles before, and there have always been these runaway factors that build on themselves (like sun's rays reflecting off of snow or being absorbed by the darker earth after the glacier has receded).  But there is always an end and subsequent reversal.

 I also like to think about the olden days, a few hundred million years ago, when there was no oil or coal in the ground.  Plants and animals were in their early stages.  Where was all of that carbon that's now locked up in coal, oil, limestone, methane in permafrost, etc.?  Probably in the air.  Before free oxygen grew in percentage, CO2 rates in the atmosphere were way higher than they are today.

I don't have time for a long reply but I just like to point out that on a global long scale you should not underestimate the role of weathering of rock on the CO2 cycle and neither the role of limestone formation or destruction.